The situation that crude oil becomes heavier is more and more severe in recent years, and the fractions with boiling points higher than 400° C. are hard to enter the pores of zeolites in crude oil. Therefore the ability of the prior zeolite-comprising catalysts to crack heavy oils cannot meet the requirements for raising the economical benefits. It has been found that the addition of layered clays to cracking catalysts can enhance the ability of cracking catalysts to crack heavy oils.
CN1031029A discloses a layer-pillared clay molecular sieve catalytic cracking catalyst, which consists of active components, support components, and binder components. The active component is a layer-pillared molecular sieve with a regular interlayer mineral structure including rectorite, or a mixture of this clay molecular sieve with other molecular sieves such as faujasite, faujasite treated by chemical and/or stabilizing treatment, or ZSM-5 series molecular sieves which accounts for 1-100%, preferably 40-60% by weight of the catalyst. The support component includes various natural clays including kaolin clay and rectorite, or various synthetic refractory oxide supports including amorphous silica-alumina, alumina, silica, or mixtures thereof which accounts for 0-99%, preferably 30-40% by weight of the catalyst. Preferably, the support component is halloysite. The binder component includes alumina sol, silica sol, silica-alumina sol and the mixtures thereof which accounts for 0-99%, preferably 10-30% by weight of the catalyst, preferably alumina sol or silica sol.
CN1031029A discloses a process for preparing the catalyst which comprises (1) mixing and forming a clay having a regular interlayer structure or a mixture of the clay and other molecular sieves, which serves as a precursor of the active component with a support component and a binder component in a ratio of 1-100:0-99:0-99 on a calcination basis; (2) formulating an inorganic metal hydroxyl polymer to a dilute aqueous solution with a concentration lower than 100 mmol Al/l and regulating the pH of the solution with NH4OH to pH 4-6 to yield a cross-linking solution; (3) adding the formed material obtained in (1) to the cross-linking solution obtained in (2) in an amount of 1.5-5.0 mmol Al per gram of the regular interlayer mineral clay in the active component and conducting the cross-linking reaction at the room temperature while maintaining the pH of the slurry at 4-6 with NH4OH; and (4) aging the slurry at 70-75° C. with stirring for 1-5 h while maintaining the pH of the slurry at 4-6, and then filtering, washing, drying, and calcining the resultant.
CN1048427C discloses a layer-pillared molecular sieve catalyst having a high olefin yield and comprising the following composition: (1) 10-50% by weight of a layer-pillared molecular sieve; (2) 4-30% by weight of a ZSM-5 zeolite modified with an element selected from the group consisting of H, Mg, RE, Zn, and P; (3) 0-15% by weight of one zeolite selected from the group consisting of β-zeolite, mordenite and ultrastable Y-zeolite; (4) 10-70% by weight of natural clays; and (5) 10-35% by weight of inorganic oxides. Said natural clay is selected from kaolin clay and halloysite. Said inorganic oxide is one or more selected from alumina, silica, and amorphous silica-alumina, the precursors of which are pseudo-boehmite, silica sol, alumina sol, and silica-alumina sol or gel thereof.
CN1048427C discloses a catalyst which can be prepared by two processes, i.e. pre-cross-linking process and post cross-linking process.
The pre-cross-linking process comprises (1) mixing and slurrying the natural clay and deionized water, acidifying the slurry by adding concentrated hydrochloric acid and stirring for 0.5-1 h, then adding the inorganic oxide or its precursor and stirring for additional 0.5-1 h to yield a support slurry comprising 10-40% by weight of solid, and (2) adding the layer-pillared molecular sieve prepared by the process of CN 86101990A and other molecular sieves, stirring the slurry for 0.5-1 h, and then forming and drying the resultant.
The post cross-linking process comprises (1) mixing, slurrying and forming the interlayer mineral structure clay as the precursor of the layer-pillared molecular sieve such as rectorite, corrensite, mica-montmorillonite, mica-vermiculite, or monolayer mineral structure clays such as montmorillonite, bentonite, hectorite, beidellite, vermiculite, the mixtures thereof with other molecular sieves and natural clays, and inorganic oxides to obtain a formed material; (2) formulating an inorganic metal hydroxyl polymer to a cross-linking solution with a concentration less than 100 mmol Al/l and regulating the pH of the solution to pH 4-6 with NH4OH; (3) adding the formed material to the cross-linking solution comprising cross-linking agent in an amount of 1.5-5.0 mmol Al per gram of rectorite, and reacting the mixture at room temperature for 5-15 min, and maintaining the pH of the slurry at pH 4-6 with NH4OH; (4) stirring and aging at 70-75° C. for 1-5 h while maintaining the pH at 4-6; (5) filtering, washing, and drying the resultant from step (4); (6) calcining the resultant from step (5) at 550-750° C. for 0.5-4 h.
CN1030376C discloses a layer-pillared clay microspherical catalyst, which has a stable macroporous layer-pillared structure and highly regularly interstratified crystalline structure, a bottom spacing d001 of up to 65×10−10 m, an interlayer spacing of up to 45×10−10 m, and an intensity of the d001 diffraction peak of up to more than 10000. The catalyst is prepared by the cross-linking reacting, forming, aging, washing, drying and calcining the mixture of the guide agent, cross-binder (in term of oxide), clay, and auxiliary component in a weight ratio of 0.1-98.0:1-98.9:1-98.9:0-97. Said guide agent is polyvinyl alcohol or an organic polymer having the formula of (—C═CHOH—)n; the cross-binder is one or more selected from the group consisting of alumina sol, silica-alumina sol, silica sol modified with polyvinyl alcohol including polymerized aluminum hydroxychloride, and zirconium sol including polymerized zirconium hydroxychloride, and copolymers or mixtures thereof; the clay is selected from the group consisting of various natural or synthetic expandable regular interlayer clay minerals including rectorite, smectite or monolayer clay minerals, and mixtures thereof; and the auxiliary component is one or more selected from the group consisting of kaolin family clays, inorganic oxide support components, sol binder components comprising aluminum, silicon, zirconium, and faujasite, ZSM-5 series zeolite active components.
CN1060204C discloses a layer-pillared clay microspherical catalyst for cracking heavy oils and the preparation process thereof, which catalyst consists of 20-90% by weight of a layer-pillared clay, 10-40% by weight of a binder with alumina as a major chemical component, 0-40% by weight of Y-zeolite, and 0-70% by weight of a kaolin family clay. Said layer-pillared clay is an expandable clay cross-linked by aluminum interlayer pillar. The precursor of said aluminum interlayer pillar is alumina sol modified with one selected from the group consisting of pseudo-boehmite, aluminum metal, NH4OH, NaOH, polyvinyl alcohol, fluorocarbon surfactant, or [Al13O4(OH)24(H2O)12]+7-containing poly hydroxyl aluminum complex. Said binder is formed by drying and calcining the precursor thereof, which may be mixtures of alumina sol and alumina gel obtained by directly peptizing pseudo-boehmite or aluminum metal by the acid obtained via hydrolysis of alumina sol after mixing and heating alumina sol and pseudo-boehmite or aluminum metal, or may be colloidal substances formed by peptizing pseudo-boehmite by adding an inorganic acid, or may also be alumina sol and/or alumina gel comprising polyvinyl alcohol or fluorocarbon surfactant or silica-alumina sol.
It can be seen that a cross-linking step for cross-linking the layered clay by a cross-linking agent to convert the layered clay to layer-pillared molecular sieve is necessary in order to obtain the cracking catalyst comprising layer-pillared molecular sieve in the prior art.
Said cross-linking agent may be an inorganic metal hydroxyl polymer (see CN1031029A, CN1048427C). When an inorganic metal hydroxyl polymer is used as a cross-linking agent, the dilute aqueous solution thereof, e.g. a dilute solution with a concentration below 100 mmol Al/l is used and the use amount is more than 20 times of that of the layered clay, which results in a considerable amount of waste liquid to be treated. Besides, when such dilute aqueous solution is used as a cross-linking agent, the pH of the slurry has to be strictly controlled between 4-6, which undoubtedly increases the difficulty in the preparation of the catalyst comprising layer-pillared molecular sieve and in the large-scale industrial production of such a catalyst. Also, this process is too complicated.
Said cross-linking agent may also be alumna sol, silica-alumina sol, or silica sol modified with polyvinyl alcohol and fluorocarbon surfactant (see CN1030376C, CN1060204C). This process does not need a considerable amount of dilute aqueous solution; however, due to the foamability and adhesivity of the polyvinyl alcohol and surfactant used, the foamability renders the dried and formed catalyst having a loose texture, low bulk density, and poor strength on the one hand, and on the other hand, the adhesivity renders the catalyst bond to the inner of the drier such as the wall of the drying tower during drying, especially during spray drying. As a result, a thick solid layer formed in the drying tower is hard to be removed and the yield of the catalyst is lowered. Another disadvantage of the process is that it is too complicated to be industrialized.
Said cross-linking agent may also be a colloidal substance formed by peptizing pseudo-boehmite with an acid (see CN1060204C). This colloidal substance needs to be prepared solely, for example, heating the slurry of alumina sol and pseudo-boehmite to 90-100° C., and the colloidal substance obtained by peptizing the pseudo-boehmite with the acid available from the pyrohydrolysis of alumina sol can act both as a cross-linking agent and as a binder. However, such process is also too complicated.
Furthermore, it is a common disadvantage of the prior catalysts that the ability for cracking heavy oils is not strong enough, so that the conversion of hydrocarbon oils and the yield of light oils are not high enough.